The present application relates to the field of radiography or computed tomography examinations and imaging. It finds particular application with pulsed imaging systems that comprise an indirect conversion detector array, such as those commonly comprised within a line scanner, mammography scanner, CT scanner, IMRT scanner, security scanner, or other radiographic imaging system.
Radiographic imaging systems provide information, or images, of an object under examination or rather interior aspects of the object. For example, in radiographic imaging systems, the object is exposed to radiation, and one or more images are formed based upon the radiation absorbed by the object, or rather an amount of radiation that is able to pass through the object. Typically, highly dense objects absorb (e.g., attenuate) more radiation than less dense objects, and thus an object having a higher density, such as a bone or gun, for example, will be apparent when surrounded by less dense objects, such as fatty tissue or clothing, for example.
Radiographic imaging systems typically comprise a detector array and a radiation source. The radiation source is generally configured to emit a fan, cone, wedge, or other shaped beam of radiation onto an object under examination. The detector array is generally positioned on a diametrically opposing side of the object relative to the radiation source and comprises a plurality of pixels configured to detect electrical charge created from radiation that impinges the detector array.
Direct conversion and indirect conversion detector arrays are two types of detector arrays commonly used in radiographic imaging systems. Direct conversion detector arrays are configured to convert x-ray photons directly into electrical charge using a photoconductor (e.g., amorphous selenium). Indirect conversion detector arrays are configured to convert radiation photons into light using a pixilated scintillator array, for example. The light can then be converted into an electrical charge using a photodetector and the electrical charge can be detected and/or collected by respective pixels of the detector array. It will be appreciated that there are numerous types of photodetectors known to those skilled in the art. For example, solid state indirect radiation detectors may comprise silicon p-i-n photodiodes as a photodetector. Other semiconductor devices can also be used, such as amorphous silicon photodiodes, CCD, etc., for example.
In such detector arrays, it is desirable to increase the detective quantum efficiency (DQE) of the detector array to improve images resulting from the examination. The DQE can be understood as the ratio of the amount of information contained in the output signal of the detector to the amount of information in the input radiation flux. The former is generally reduced due to imperfections of the detector array, including electronic noise, nonuniformity of the output, nonlinearity, etc., for example. Moreover, in indirect conversion detector arrays, the DQE can be negatively affected by parasitic contributions (e.g., due to an increase in so-called Swank noise) that are caused by x-ray photons that interact directly with the photodiode without interacting with the scintillator material (e.g., the x-ray photons are not converted to light before being converted into electrical charge).